Space and time are therefore to be regarded as the necessary _a priori_ pre-conditions of the possibility and reality of all phenomena. It is clear that transcendental æsthetic can obtain only these two elements, space and time, because all other concepts belong to the senses and pre-suppose experience, and so imply something empirical. For example, the concept of motion pre-supposes something moving, but in space regarded alone there is nothing that moves; therefore, whatever moves must be recognised by experience, and is a purely empirical datum. _II.--Transcendental Logic_ Our knowledge is derived from two fundamental sources of the consciousness. The first is the faculty of receptivity of impressions; the second, the faculty of cognition of an object by means of these impressions or representations, this second power being sometimes styled spontaneity of concepts. By the first, an object is given to us; by the second it is thought of in the mind. Thus intuition and concepts constitute the elements of our entire knowledge, for neither intuition without concepts, nor concepts without intuition, can yield any knowledge whatever. Hence arise two branches of science, æsthetic and logic, the former being the science of the rules of sensibility; the latter, the science of the rules of the understanding. Logic can be treated in two directions: either as logic of the general use of the understanding, or of some particular use of it. The former includes the rules of thought, without which there can be no use of the understanding; but it has no regard to the objects to which the understanding is applied. This is elementary logic. But logic of the understanding in some particular use includes rules of correct thought in relation to special classes of objects; and this latter logic is generally taught in schools as preliminary to the study of sciences. Thus, general logic takes no account of any of the contents of knowledge, but is limited simply to the consideration of the forms of thought. But we are constrained by anticipation to form an idea of a logical science which has to deal not only with pure thought, but also has to determine the origin, validity, and extent of the knowledge to which intuitions relate, and this science might be styled transcendental logic. In transcendental æsthetic we isolated the faculty of sensibility. So in transcendental logic we isolate the understanding, concentrating our consideration on that element of thought which has its source simply in the understanding. But transcendental logic must be divided into transcendental analytic and transcendental dialectic. The former is a logic of truth, and is intended to furnish a canon of criticism. When logic is used to judge not analytically, but to judge synthetically of objects in general, it is called transcendental dialectic, which serves as a protection against sophistical fallacy. ANALYTIC OF PURE CONCEPTS